1. Field of the Invention
The present invention relates to an ion generating apparatus constituting an ion implantation apparatus.
2. Description of the Related Art
FIGS. 3A and 3B are schematic diagrams each illustrating an example of a conventional ion generating apparatus. As illustrated in FIG. 3A, an ion generating apparatus 9 includes: a chamber 7; a cathode 8 for generating thermal electrons within the chamber; a filament 1 arranged outside of the chamber 7 and in the vicinity of the cathode 8; a direct-current power supply 2 connected in series to the filament 1; a gas introduction port 5 for introducing gas into the chamber 7; and an ion beam take-out port 6 for taking out ions generated within the chamber 7 to the outside of the chamber. In FIG. 3B, the filament 1 is arranged in the inside of the chamber 7.
In an ion implantation apparatus, when ion implantation process is performed in which fluorine compound gas such as boron trifluoride (BF3) is used as ion source gas, a deposit containing fluorine generated from the fluorine compound gas is deposited in the above-mentioned ion generating apparatus, a source housing, and the like. In order to clean the ion generating apparatus, the source housing, and the like, it is necessary to expose the ion generating apparatus, the source housing, and the like to the atmosphere. However, the deposit containing the fluorine and moisture contained in the atmosphere react with each other to generate hydrogen fluoride (HF), and hence there is a fear of dispersion of vapor containing HF within a clean room.
In order to prevent the dispersion of the vapor containing HF into the clean room, the following counter-measure has been taken. For example, the source housing is purged with the atmosphere before the source housing is vacuumed with a vacuum pump, and then the above-mentioned atmosphere purge step is repeated, and hence the amount of the deposit containing the fluorine decreases. Otherwise, a channel through which the atmosphere containing HF vapor is discharged is provided with a discharge channel including a gas cleaning device and with a suction and discharge pump (for example, see Japanese Patent Application Laid-open No. 2001-167728 and No. 2001-167707).
Meanwhile, the following fact is empirically known. When an ion implantation process using hydride gas such as phosphine (PH3) is performed after an ion implantation process using the fluorine compound gas such as BF3, a reduction reaction is achieved between hydrogen ion generated through ionizing the hydride gas and a deposit containing the fluorine to make HF vapor, which is discharged by the vacuum pump, decreasing the deposit containing the fluorine. Accordingly, the following process is also effective. Specifically, before exposed to the atmosphere, the hydride gas is ionized to generate the hydrogen ion and is introduced into the source housing, and then introduction of the hydride gas is stopped and inert gas such as argon (Ar) gas is in turn introduced therein. In this way, concentration of the hydride gas is lowered. After that, the atmosphere purge is performed.
In the ion implantation apparatus in which the fluorine compound gas such as BF3 and the hydride gas such as arsine (AsH3) or PH3 are introduced as ion source, it is effective that, before exposed to the atmosphere, the hydride gas is ionized and is caused to react with the deposit containing the fluorine deposited in the source housing and the like, to thereby remove the deposit. By the way, as one example case of exposure to the atmosphere, in order to interchange a cathode filament if the cathode filament is broken, the source housing may be exposed to the atmosphere. As a case where the cathode filament is broken, there is a case where the cathode filament is broken during ion implantation using the hydride gas, or a case where the cathode filament is broken during ion implantation using the fluorine compound gas. In the case where the cathode filament is broken during ion implantation using the hydride gas, introduction of the hydride gas is stopped and exposure to the atmosphere is performed through substituting the inert gas or the atmosphere for the hydride gas. Meanwhile, in the case where the cathode filament is broken during ion implantation using the fluorine compound gas, it is impossible to introduce the hydride gas in place of the fluorine compound gas so as to ionize the hydride gas. With this regard, the present invention provides a method of removing the fluorine compound deposited in the source housing and the like through ionizing, after the cathode filament is broken, the hydride gas under a state in which the cathode filament is broken.